ON SOME WATER-WOEN AND PEBBLE-WORN STONES. 63 



6. On some Water-worn and Pebble-worn Stones tdkenfrom the 

 Apron of the Holt-Fleet Weir on the River Severn. By 

 Henry John Marten, Esq., M.Insb.C.E., P.G.S., Engineer to 

 the Severn Commissioners. (Eead December 10, 1890.) 



In the year 1844 a weir was constructed by the Severn Commis- 

 sioners across the Eiver Severn at a place called Holt Fleet, about 

 eight miles above the city of Worcester, with the object of impound- 

 ing the water above it, for navigation purposes, to a height of 5 feet 

 4 inches above previous low summer-level. 



The weir, a plan and section of which accompany this paper 

 (figs. 7 & 8), is a dam of solid masonry across the river, without any 

 sluices in it ; so that the whole of the water passing down the 

 river at that point flows over the crest of the weir and down the 

 slope, or face of the apron, on its lower side. 



The crest of the weir is 300 feet in length, and the drainage from 

 1870 square miles (nearly 1,200,000 acres) of country above it, 

 extending to the Plinlimmon range, is discharged over it. 



The stones of which the weir is constructed were taken from an 

 adjoining quarry at Holt Fleet, and consist of a soft red sandstone 

 of the Upper New-Red- Sandstone Formation, marked F. 5 on the 

 one-inch map of the Geological Ordnance Survey. 



In the year 1887, or 43 years after the stones were placed 

 on the apron of the weir, an examination was made of them, as 

 some of the stones had become displaced and others showed signs of 

 decay. 



The examination brought to light the fact that a large proportion 

 of the stones on the Island side of the central portion of the apron of 

 the weir had been drilled through and through by the action of the 

 current upon small pebbles lodged either in hollows on their exposed 

 surfaces, or between the joints of the stones *. 



A table is appended (page 67) giving various particulars of each of 

 the photographed stones (figs. 1-6) — namely, the dimensions, cubic 

 contents, and estimated weight of each stone when placed in the weir, 

 and the cubic contents and weight of each stone when removed from 

 the weir, together with the percentage of loss during the period of 

 43 years, and the average annual loss during that time. 



In order to estimate the weight of each stone when placed in the 

 weir, a piece of one of the stones, which was an average sample of 

 the whole — and they were throughout of a uniform character — was 

 cut exactly to a six-inch cube ; that is, to one eighth of a cubic 

 foot. 



This six-inch cube, after saturation in water for three hours, 



* A sample of a portion of one of these stones, accompanying this paper, 

 together with a set of photographs (here reproduced, at the Author's expense, 

 figs. 1-B) of six of the stones themselves, were exhibited when the paper was 

 read. In nearly all the photographs the small pebbles referred to are shown 

 in situ, as they were found. 



